Crystal beat-frequency oscillator



Aug. 31, 1948. M. MORRISON 2,

CRYSTAL BEAT-FREQUENCY OSCILLATOR I Fil ed July 19, 1945 INVENTORPatented Aug. 31 1948 UNITED STATES PATENT OFFICE CRYSTAL BEAT-FREQUENCYOSCILLATOR Montford Morrison, Upper Montclair, N. J Application July 19,1945, Serial No. 605,885

Claims. 1 v

The present invention relates to electronic tube oscillators, moreparticularly to beat-frequency electronic tube oscillators andspecifically to piezo-electric crystal controlled beat-frequencyelectronic tube oscillators.

An object of the invention is to provide a beatfrequency oscillatoremploying but a single tube and having a high order of beat-frequencystability.

Anotherobject of the invention is to provide a crystal controlledoscillator operating at frequencies, which in the prior art require acostly bar of piezo-electric crystal material, but which,

by the mployment of the present invention, oper ate with two very thinand very inexpensive crystals in quantity production.

A further object of the invention is to provide a crystal controlledsingle tube oscillator for frequencies below the range of practicalsingle-bar crystal-controlled oscillators.

By the employment of the present invention, the lower range ofcrystal-controlled oscillators is not only extended below the practicalrange of prior art crystal-controlled oscillators, but fur-- ther,provides a simple and inexpensive crystalcontrolled oscillator withinthe present low ranges requiring bars of crystals. For instance, by theemployment of this invention, primary oscillation frequencies may beobtained simply and inexpensivelyfor oscillators in theaudiobeat-frequency range. Under prior art structure, a primaryfrequency oscillator for an audio beat-frequency system would require abar of quartz crystal of the magnitude of about 3 centimeters long withthe accompanying expensive crystal holder and other auxiliary fittings.With the present invention, a beat-frequency oscillator may beconstructed employing two crystals of say 1% the thickness of the lengthof the bar mentioned above and which thin crystals are now in productionin large quantities and which may be produced at a very small fractionof the cost of the single bar.

It will be appreciated that exact frequencies are not required in abeat-frequency oscillator, since it is only the difference frequencywhich needs to be exact; suitable crystals may be selected in pairs fromlarge runs of crystal manufacture without the necessity of grinding anyone particular crystal to a high degree of accuracy. In furtherexplanation of this point, it may be said that a single bar ofpiezo-electric material ground and/or etched to a high degree ofaccuracy for say 100,000 cycles, is a very expensive procedure. However,if a large number of crystals are ground, say in the vicinity of 3millimeters without requiring that the frequencies be very exact, thecost of such thin crystals is a very small fraction of that of thesingle highly accurately made bar. With considerable production, it ispracticable to select pairs of approximately ground crystals which havea frequency difference of 100,000 cycles, to a good degree of practicalaccuracy. In any case, the final grinding or etching of a single unit ofa pair of such thin cfiystals is a comparatively inexpensive procedure.

The lower practical limit of quartz oscillator bars is about 20,000cycles, and it will be obvious to those skilled in the art that by theemployment of the present invention, this lower limit may not only beextended but at a cost greatly under that of a 20,000 cycle bar, which,it will be remembered, requires a very special holder which costs asmuch as a considerable portion of the cost of the bar itself.

The applicant appreciates that the operative results of his inventionmay be accomplished by a combination of two separate and completeoscillators employing two tubes and two plate circult oscillatorysystems and the nature of the present invention resides in the novelstructure disclosed, which employs but a single tube and a single platecircuit oscillatory system which, it is believed, is a distinctimprovement in the art.

The spirit of the present invention does not reside in the employment ofany particular type of tube and is independent of the number ofelectrodes contained in the tube and independent of which electrodes areemployed for what purpose, provided of course, that the structure inquestion is Within the meaning of the recitation of the claimshereunder.

The nature of the invention resides in a structure which employs twopiezo-electric crystal oscillatory systems connected to a singleelectronic space discharge tube having a single capacitive inductiveoscillatory output circuit in such a structural form that both of thefrequencies of the two crystal oscillatory systems are simultaneouslypresent in the single output capacitive-inductive oscillatory system.

A very large number of structures may be made, employing the spirit ofthis invention, by the use 'of'multielectrode tubes employing more thanone grid for control purposes, structural differences in feed-backarrangements and various other modifications, extensions and changes,but it is believed that the invention can be best taught to thoseskilled in the art by the disclosure of one of the very simplestembodiments of the invention aees, 188

since the use of multi-electrode tubes, beam power tubes, internal andexternal feed-back circuits and the like are well known to those skilledin the art. The specific nature of the invention will be understood byreference to the description hereunder, particularly when taken inconnection with the drawing.

In the figure, I is a triode having an anode 2, a grid 3 and a cathode4. A piezo-electric crystal 5 is connected between the anode 2 and thegrid 3 and which crystal may be thrown out of circuit by opening switch6.

The grid cathode circuit is shunted by a resistor l which is providedwith a bias generator 33 which may be shunted by a condenser 9. Thecathode grid circuit is further shunted by a second piezoelectriccrystal Iii which may be thrown out of circuit by opening switch I I.

Tube l is provided with a source of anode energy i2 which may be shuntedby condenser I3 and energy is fed from source i2 through thecapacitive-inductive oscillatory system M to anode 2. The oscillatorysystem M is coupled to a detector l5, if and when desired.

The operation of the invention will now be disclosed.

By opening switch 6, it will be observed by those skilled in the artthat in the absence of any operation on the part of crystal 5, that thecircuit is that of a common type of crystal-controlled oscillator inwhich the feed-back from the anode circuit is provided by the capacitivecoupling between anode 2 and the grid 3.

It is well known in the art that such a circuit, that is, as illustratedby the figure with switch 6 open, requires that the feed-back to thecrystal Ill be from an anode circuit system such as M which is inductiveto the frequency of the natural period of crystal i0, that is, theoscillatory circuit l4 must be tuned to a natural frequency slightlyhigher than that of the natural period of crystal l6.

Further, if switch 6 be closed and switch H be opened, it is obvious tothose skilled in the art, that the diagram under these conditionsdiscloses a common type of crystal-controlled oscillator in which thecontrol crystal is operated by direct feed-back from the anode circuit,and further, it is well known in the art that such a crystal-controlledoscillator requires that the feed-back energy for crystal 5 be suppliedfrom an oscillatory circuit M which is capacitive to the naturalfrequency of the crystal ii, or in other words, circuit l4 must be tunedto a slightly lower frequency than that of the control crystal 5.

The applicant has discovered that by closing both switches ii and H andby properly choosing the frequency difference between crystals 5 and It,he can adjust circuit M so that the circuit H5 is simultaneouslyinductive to the frequency of crystal l and capacitive to the frequencyof crystal '5 and thus is able to provide with a single tube and asingle anode oscillatory system the complete requirements for excitationof both crystals and id, simultaneously.

The Q of the circuit l4 must be considerably lower than that of crystals5 and lil, so that cir cuit i4 is capable of oscillation withconsiderable amplitudes at both the frequencies of crystals 5 and i9.

With the simultaneous operation of crystals 5 and Ill, both frequenciesthereof are produced in the oscillatory system is simultaneously andtherefore the beat-frequency of crystals 5 and i0 appears in the outputcircuit I4.

The present invention is distinguished from oscillating detectors andregenerative detectors by the fact that these detectors feed back onlyone frequency to the input circuit thereof, that the beat-frequency isgenerated in a single capacitive-inductive input circuit, and not in theoutput circuit, and further, that if crystal control is resorted to inoscillating detectors, only one crystal may be employed locally andobviously no feed-back can be said to exist between an oscillatingdetector and a crystal control in a remote transmitter. Many otherstructural differences exist which are obvious to those skilled in theart.

single space discharge electronic tube having a cathode, a grid and ananode; comprising a tube having a piezo-electric oscillatory crystalcircuit coupled between the cathode and grid thereof. a secondpiezo-electric oscillatory crystal circuit coupled between the anode andgrid of said tube, a single capacitive-inductive oscillatory circuit asource of anode energy connected between the anode and cathode of saidtube, and means to feed back energy from the singlecapacitanceinductance oscillatory circuit to both said crystal circuits.

2. In a beat-frequency oscillator, a space discharge electronic tubehaving input electrodes including a cathode and a control grid andoutput electrodes including said cathode and an anode, a source ofelectrical energy connected to last said electrodes, acapacitance-inductance oscillatory circuit coupled to said outputelectrodes, two oscillatory systems connected to said grid, each of saidsystems having a natural period of oscillation different from that ofthe other of said systems, each of said systems being fed back withenergy from the oscillatory circuit coupled to said output electrodesunder reactively different couplings, and the combined frequencies ofboth said systems being generated in said oscillatory circuit.

3. In a beat-frequency oscillator, a space discharge electronic tubehaving input electrodes including a cathode and a control grid andoutput electrodes including said cathode and an anode, a source ofelectrical energy connected to last said electrodes, a singlecapacitance-inductance oscillatory circuit coupled to said outputelectrodes, two oscillatory systems connected to said grid, each of saidsystems having a natural period of oscillation different from that ofthe other of said systems, each of said systems being fed back withenergy from the single oscillatory circuit coupled to said outputelectrodes under reactively different couplings, and the combinedfrequencies of both said systems being generated in said singleoscillatory circuit.

4. In a beat-frequency oscillator, a space discharge electronic tubehaving input electrodes including a cathode and a control grid and out-.put electrodes including said cathode and an anode, a capacitancednductance oscillatory circuit coupled to said outputelectrodes, a crystal oscillatory system having a predetermined naturalperiod and connected to said grid, said oscillatory system having afeed-back from said oscillatory circuit reactively inductive to saidnatural period, a second crystal oscillatory system having a naturalperiod different from that of first said crystal oscillatory system andconnected to said grid, second said oscillatory system having afeed-back from said oscillatory ci-rcuit reactively capacitive to saiddifferent natural period, and a source of electrical power connected tosaid oscillatory circuit providing energy to said feed-backs.

5. In a beat-frequency oscillator, a space discharge electronic tubehaving input electrodes including a cathode and a control grid andoutput electrodes including said cathode and an anode, a singlecapacitance-inductance oscillatory circuit coupled to said outputelectrodes, a crystal oscillatory system having a predetermined naturalperiod and connected to said grid, said oscillatory system having afeed-back from said single oscillatory circuit reactively inductive tosaid natural period, a second crystal oscillatory system having anatural period diiferent from that of first said crystal oscillatorysystem and connected to said grid, second said oscillatory system havinga feed-back from said single oscillatory circuit reactively capacitiveto said different natural period, and a source of electrical powerconnected to said single oscillatory circuit providing energy to saidfeed-backs.

6. In a beat-frequency oscillator, a space discharge electronic tubehaving input electrodes including a cathode and a, control grid andoutput electrodes including said cathode and an anode, a source ofelectrical energy connected to said output electrodes, two crystaloscillatory systems having a predetermined beat-frequency coupled tosaid grid, a capacitance-inductance oscillatory circuit coupled to saidoutput electrodes and feeding back energy through different couplinpaths individually to said two crystal oscillatory systems, saidoscillatory circuit having said beat-frequency generated therein byreaction of said tube, and a detector means coupled to said oscillatorycircuit providing an alternating current of said beat-frequency.

7. A beat-frequency oscillator comprising, a single space dischargeelectronic tube having input electrodes including a cathode and a,control grid and output electrodes including said grid and an anode, twopiezo-electric oscillatory crystals electrically connected in series andelectrically coupled at the intermediary connection to said grid, saidtwo crystals having difierent natural periods of oscillation, acapacitive-inductive oscillatory circuit coupled to said outputelectrodes and having a natural period of oscillation in between theperiods of oscillations of said two tals under reaction thereof withsaid tube, a

source of electrical energy connected to said output electrodes, andmeans to feed a part of said energy through different coupling pathsback to both said crystals providing independent driving energy for eachcrystal.

9. A beat-frequency oscillator comprising a single space dischargeelectronic tube having electrodes including a cathode, a grid and ananode, in combination a piezo-electric oscillatory crystal circuitcoupled to two of said electrodes requiring feed back reactivelyinductive to the frequency thereof to maintain oscillation therein underoperation, a second piezo-electric oscillatory crystal circuit coupledto two of said electrodes requiring feed back reactively capacitive tothe frequency thereof to maintain oscillation therein under operation, asingle capacitive-inductive oscillatory circuit coupled to two of saidelectrodes and providing reactively inductive feed back to first saidcrystal circuit and reactively capacitive feed back to second saidcrystal circuit, and a source of electrical energy connected to saidcapacitive-inductive oscillatory circuit providing feed back energy tosaid crystal circuits.

MON TFORD MORRISON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,559,116 Morrison Oct. 27, 19251,780,229 Green Nov. 4, 1930 1,830,322 Hund Nov. 3, 1931 2,288,486Rivlin June 30, 1942

